NMA FOUR STROKE SILENCER TEST

Local off-road association puts after-market pipes through
the ringer

By Sean Callahan

The 2002 season began with an emphasis on limiting sound emissions at all NMA
Competition events, including Poker Runs. The NMA has for some time posted
limits of 98db for water-cooled and 102db for air-cooled bikes with limited
enforcement. The expectation was for self-compliance, each rider doing his/her
part maintaining their equipment to help preserve our riding opportunities.

However, with the growing popularity of racing 4-strokes, excessive sound is
now a real reason for concern. 4-stroke engines produce a low resonance that
travels further than its 2-stroke cousin. With eco-extremists pushing ever
harder to close our riding/racing opportunities, we cannot afford to allow a
nuisance that is controllable give the enemy more ammunition.

Earlier this year, a team of volunteers worked together to monitor and test
for sound emissions at most NMA events. We chose to use the 2002 season as an
advisory year to educate the riders and clubs, with 2003 as an enforcement
season. While most bikes and riders had no problem meeting the NMA sound
standard, a few were confused. Several times, the question came up as to which
after-market company made a muffler that would meet the NMA Sound Standard. That
is when the realization hit home, who wants to spend $300+ hard earned cash on
an exhaust that won't pass!

I began researching the ads in 2 popular off road magazines. None of the
companies advertised their sound output, just that they were quiet, forestry
approved, off road systems. So the next step was to contact the companies direct
and start asking questions, all of which were polite and helpful. Eventually,
this led to the conclusion that we needed to do our own testing.

The Monroe Motocross Club private track was selected as the testing site. It
features a 7/8 mile MX track with 2 uphills and a 5 mile off-road course. Next,
we assembled a group of riders with varying skill levels to evaluate the pipes.

Sound testing was conducted with the same (MIC) stationary format used at NMA
events. Curt Emmerson manned the sound meter and Sean Callahan operated the
sirometer (vibra-tach).

The testing format involved each test rider on the stock bike for several
laps on the track noting performance. Then we sound tested the stock pipe before
mounting a new test pipe and repeating the same laps, again followed by a sound
test and performance evaluation. Each pipe was given a rating for sound and
power on a scale from 1 thru 5 with 5 as best, 1 as worst. Then an overall
rating scale of A for best, an F for worst with an emphasis on sound. The
following results are the combined efforts from 8 riders and 7 bikes.

Honda CRF 450R - Stock 97db We were impressed with Hondas 4-stroke MX sound
level in comparison to the power. However, to race this machine on public (or
leased) land, you need a spark arrestor, so replacement is mandatory! Also,
remember that this is a full blown moto machine - off road pipes will affect
power.

FMF Q - 97db. Power off bottom is softer, mid range same as stock, softer on
top with rev out signed off earlier. Softer power output could benefit most
riders in tight, technical off-road racing (Gold Bar, Mt.Baker). Sound - 3 Power
- 3 Overall - C Overall rating suffered from acceptable but higher than hoped
db. With the power changes, sound should be lower - still good option.

Pro Circuit T-4 - 95db (Quiet Core insert & 1.5" end cap required)
Power off bottom softer than stock, mid to top very close to stock. Rev out very
good. Softer power delivery off bottom is benefit in off-road events for most
riders. The power is softer for places like Gold Bar, but also retains good top
end for Rimrock. Good balance. Sound - 4 Power - 5 Overall - A-

White Bros. E Series - 97db (9 disks as delivered). Off idle to mid range
increase, top end signs off early. Good performance increase over stock - might
be more technical in slippery, tight sections for some riders. Misc. notes -
mounting position rubs on tire at full compression, can be quieter by removing
disks and could soften power delivery as well. Sound - 3 Power - 4 Overall - B-
Overall rating is due to the ability to make the system quieter.

KTM RFS 520 SX Stock 94db. KTM never ceases to amaze us, a MX version that
produces only 94db! To race off-road, you need a spark arrestor even if it is
quiet enough.

KTM RFS 400EXC - Stock 89db. KTMs versatile woods bike performs excellent in
stock trim. We wanted to see if there were any improvements to be had without
sacrificing a very stealthy racing machine.

FMF Q - 92db. Power increase over entire rpm range. Pulls longer on top than
stock. Still retains tractable characteristics, but more power when needed.
Still in the stealth range. Sound - 5 Power - 5 Overall - A

KTM RFS 450EXC - Stock 90db. KTMs new woods weapon has a noticeable mid-range
boost over the replaced 400 among other new enhancements. Along with the
increase in power, came a small increase in sound, interesting.

FMF Q - 92db. Power increases right off bottom, mid-range pulls harder, pulls
longer on top than stock. Still retains tractable characteristics, but may
require a little finesse with slick conditions. Still in the stealth range.
Sound - 5 Power - 5 Overall - A

Overall ratings for the 400/450 are high due to the performance gains versus
the slight increase in sound. These results are what most pipe buyers would
expect.

Suzuki DR400 - Stock 91db. A very quiet ride in stock trim, could use a
little boost in the pony department. Curt Emmerson didn't know that his well
planted DR could clear a 50' tabletop!

FMF Q - 94db. Good response off bottom, more mid to top performance, pulls
longer, harder. Overall better throttle response. Very good trade-off between
sound and power gain. Good replacement. Sound - 4 Power - 5 Overall - A

Yamaha WR250F - Stock 88db. The stock pipe is very quiet, but because of the
small displacement most riders want more power. These mid size 4 strokes (Honda,
KTM, Suzuki/Kawasaki have plans for releases soon) pose the biggest challenge in
producing more power without excessive sound levels. The stock pipe on the WR is
very restrictive so opening it up helps considerably.

FMF Q - 94db. Power increases right off idle, pulls through the mid range and
continues to pull hard up on top. Retains the very tractable characteristics
this motor is known for, just more power everywhere. Excellent replacement.
Sound - 4 Power - 5 Overall - A

White Bros. E Series - 96db. (13 disks as delivered) Power gain throughout
rpm range. Power builds from bottom all the way through top. Sound - 3 Power - 4
Overall - B- Overall score was lower due to noticeably loud "on track"
sound (louder than the stationary test indicates) - more so than other pipes.
Removal of a few disks could help.

Yamaha WR400F - Stock 99db. The stock pipe is LOUD so we were looking to
quiet this beast.

FMF Q - 97db. Power was good off bottom through mid, top end similar to
stock. The Q did reduce the sound, but we would like to see a better (lower)
level. Sound - 4 Power - 3 Overall - B-

CRD is a new entry in aftermarket pipe offerings in the States. The products
are made in France with the US importer, Ligne Racing (pronounced 'line')
located in Indiana. During our testing, it became apparent that the CRD pipes we
were testing were not US Forestry Spark Arrestor approved (in Europe, spark
arrestors are not required). Eric Gauthier at Ligne Racing informed us that the
Forestry approval was in the works and pending. Because spark arrestors are
mandatory, we had to separate CRD from the pipes that have approval. We hope to
retest CRD pipes in the near future as soon as the US Forestry grants their
approval. Here are the results -

KTM RFS 520SX

CRD Absolute Performance - 92db. Very quiet with noticeable decreases in
overall power output. Softer bottom through an early sign-off on top. Can be
beneficial on slick surfaces and very technical sections. Very stealthy. Not
Forestry Approved at time of test. Sound - 5 Power - 2 Overall - C Overall
rating is middle of the road due to low sound but some riders may not like the
softer power. KTM RFS 400/450 EXC

CRD Absolute Performance - 88db Very quiet with noticeable decreases in
overall power output. Softer bottom through an early sign-off on top. Can be
beneficial on slick surfaces and very technical sections. Super stealthy. Not
Forestry Approved at time of test. Sound - 5 Power - 2 Overall - C With the
stock muffler at 89db, this pipe slightly lowers the sound, but at a sacrifice
of some throttle/power response. Because this is a 400, some riders may be
looking for more power with a replacement pipe.

Suzuki DR400

CRD Absolute Performance - 91db. Substantial gains in power, throttle
response throughout the rpm range with good top end pull. Retains good
tractability, but pulls hard without sacrificing stealth. Not Forestry Approved
at time of test. Sound - 5 Power - 5 Overall - A

Yamaha WR400F

CRD Absolute Power II - 96db. Better throttle response,
power gains throughout rpm range with good top end pull - better than stock,
quieter than stock, good improvement. Not Forestry Approved at time of test.
Sound - 4 Power - 5 Overall - A Overall score reflects the benefit of lowering
the sound on this difficult bike, while increasing performance.

Miscellaneous Notes

FMF - The Q pipe construction is lightweight, sturdy and nicely finished.
Installation for some models took a few minutes longer than other pipes and
required 2 people, but the fit was good. Mounting hardware and instructions were
complete.

Pro Circuit - The T-4 with the Quiet Core insert is lightweight, sturdy and
looks good. The only bike tested was the Honda CRF450R, the fit and installation
was super clean and easy (clamp-less slip-on).

White Brothers - The E-Series fit and finish is very good. The pipe is
lightweight and durable. On the Honda, the mount position allowed some tire
rubbing at full compression. The ability to remove disks to reduce sound is an
interesting option. Mounting hardware and instructions were complete.

CRD - The construction is stainless steel so they are heavier than the other
pipes. Long term durability is the goal according to Eric at Ligne Racing. The
polished stainless is very nice looking. Installation is simple, instructions
are okay. With US Forestry approval pending, call and get info from Eric to
ensure compliance before purchase.

Summary

The intent of this research is to give guidelines on what is available to NMA
members. We contacted the companies that represent our industry (off-road) best.
Of those listed at the beginning, only Yoshimura declined. Their response can be
read at the end of this article. The methods used during this test were designed
to be the most accurate, real world scenario to achieve our results. Your
impressions may be different, and/or you may disagree with our findings. We hope
that this information is of use to you in making a decision on which pipe to
buy. Good Luck!

We would like to thank the riders and bike owners who spent their personal
time in helping prepare this evaluation -

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